Resolve some linter warnings

[swift-kim]

Resolve some warnings generated by clang-tidy to meet the Google C++ style convention.

• Add missing braces.
• Convert C-style casts to C++-style casts (static_cast, reinterpret_cast). Return types of some functions (e.g. GetImageHandle) were changed as necessary.
• Format TODOs.

There only remain 4 warnings now. I'm not going to fix them right now.

How to run clang-tidy:

1. Add this line to the .clang-tidy file.

   WarningsAsErrors: 'google-*'
   

2. Replace calcTidyPath(firstCommand) with 'clang-tidy-11' in ci/bin/lint.dart.
3. Run ci/lint.sh.

[bbrto21]

LGTM

[swift-kim]

I'll resolve conflicts when #86 is merged.

[swift-kim]

Rebased and added a commit related to TextInputTypeToEcoreIMFInputPanelLayout.

❌ Failures for clang-tidy on /home/swift/Git/engine/src/flutter/shell/platform/tizen/channels/text_input_channel.cc:
/home/swift/Git/engine/src/flutter/shell/platform/tizen/channels/text_input_channel.cc:63:35: error: non-const reference parameter 'panel_layout', make it const or use a pointer [google-runtime-references,-warnings-as-errors]
    Ecore_IMF_Input_Panel_Layout& panel_layout) {

[bbrto21]

Rebased and added a commit related to TextInputTypeToEcoreIMFInputPanelLayout.

❌ Failures for clang-tidy on /home/swift/Git/engine/src/flutter/shell/platform/tizen/channels/text_input_channel.cc:
/home/swift/Git/engine/src/flutter/shell/platform/tizen/channels/text_input_channel.cc:63:35: error: non-const reference parameter 'panel_layout', make it const or use a pointer [google-runtime-references,-warnings-as-errors]
    Ecore_IMF_Input_Panel_Layout& panel_layout) {

Reference : https://stackoverflow.com/questions/26441220/googles-style-guide-about-input-output-parameters-as-pointers/26441753#26441753